No abstract

ABSTRACT. Meridional cross sections of the concentration of light hydrocarbons are reported. They were obtained from 20. April to 10. May, 1980, during the French research flight STRATOZ 11, and cover the latitudes between 60 0 Nand 60 0 S and the altitudes between 800 mb and 200 mb. The mixing ratios of ethane, ethene, acetylene, propane, propene, n-butane, i-butane, n-pentane, and i-pentane range between 2.0 and 0.02 ppb. Globally, a decrease in concentration with increasing altitude and -in most cases -with decreasing latitude is observed. In addition the 2-dimensional concentration fields show structures of different scales. In particular, isolated maxima of high concentrations are found in the upper troposphere. They paint to fast vertical transport between the boundary layer and the upper troposphere. In the present case these maxima seem to be correlated with large scale meteorological systems, such as low pressure regions Or the Inter Tropical Convergence Zone. It is argued that the NMHC provide a set of tracers well suited to the detection of fast vertical transport.

During the STRATOZ III flights in June 1984, approximately 160 measurements of peroxyacetylnitrate (PAN) were made with a specially designed gas chromatograph on board the Caravelle 116 airplane. The measurements cover a latitude range from 70øN to 60øS and altitudes up to 12 km. The results show that PAN is present throughout the troposphere at low but measurable levels. Southern hemispheric data from clean marine air masses show levels of 7-10 ppt, with little variability up to about 10 km altitude. In the southern uppermost troposphere and lowest stratosphere a significant increase in PAN can be seen, indicating substantial in situ formation of PAN at these altitudes. The situation at lower latitudes in the northern hemisphere is similar as long as the air masses are free of anthropogenic influence. At mid and high northern latitudes, considerably higher PAN mixing ratios (sometimes more than 100 ppt) are found even outside continental areas. These data also show a rather high variability. This can be ascribed to the influence of North America and Europe as source areas for PAN and PAN precursors.